This invention relates to an electrolyzing method and an electrolytic cell using a fluidized bed for various electrochemical reactions such as recovery or refining of various metals, electroplating to granules and decomposition of organic compounds and/or cyanic compounds.
Fluidized bed electrolysis employing fluidized electrode particles, such as metal particles, for the recovery of metals in solution or electroplating to granules has been known (U.S. Patent Specification Nos. 3,457,152 and 4,212,722) Prior to the development of this fluidized bed electrolysis, the following methods had been employed to recover metals in solution.
(a) Adding a reducing agent to the metal containing solution to deposit metals directly from the solution.
(b) Introducing the solution containing metal ions and/or metal cyanide complex ions to a tower filled with ion exchange resins to fix the metal ions, metal-cyanide complex ions on the ion exchange resins.
(c) Electrolyzing solution at a low current density in an electrolytic cell to deposit metals on a cathode.
These methods, however, have the following disadvantages. Although metals can be recovered thereby from the solutions, method (a) has the disadvantage that since a large quantity of solution must be employed, the reaction requires a long time and the operation cost is high. Although the operation of method (b) itself is easy, the construction cost of the equipment and operation cost of chemicals for regeneration are high. Method (c) is suitable for waste solutions containing high concentrations of gold, but a reduced current density is necessary to obtain an economical current efficiency when the waste solution has a low gold concentration. This makes the electrolytic cell larger and of high construction cost. Further, since a low current density operation is utilized, the metal is deposited as an extremely good plating so that, in practice, it is necessary to use a parting agent for redissolving the metal because the usual method of removing the metal from the cathode is difficult to use.
These methods have been applied, not only for the recovery of metal from solutions, but also to processes in which metal containing a small quantity of impurities is refined to high purity metal or a desired metal is electro-plated onto granules, and similar disadvantages have been found therein.
The fluidized bed electrolysis technique has been developed in order to overcome the above disadvantages.
The technique has enabled metals to be deposited on electrode particles at a high current efficiency and a low electrolytic voltage by accomodating the fine electrode particles in an electrode chamber in which an electrolyte is electrolyzed, and fluidizing the particles by the electrolyte alone, or the electrolyte and supply gas.
However, since in conventional fluidized bed electrolysis, a plate-like electrode is employed as an opposite electrode, the following disadvantages are pointed out. A gas generated in an opposite electrode chamber comes between the opposite electrode and a diaphragm separating th two electrode chambers from each other, making the electrolysis condition unstable by raising the electrolytic voltage, or bending the diaphragm to damage it. Moreover, if the degree of curvature of the diaphragm is excessive, it prevents fluidization of the particles and makes the electrolysis condition more unstable.